MFJ-918WM, MFJ-2919WM, and MFJ-2920WM
1.5 kW, 1.8-30 MHz Wall-Mount Balun
Introduction:
Without a balun, the outer surface of your coax shield provides a common-mode
path for transmitted RF to flow from the antenna down to your operating location. Here, it can
disrupt or damage sensitive electronics and, if severe, may even change the antenna's radiation
pattern, distort your transmit audio, or cause a painful RF burn. On receive, the process is
reversed, with stray locally generated carriers and "hash" traveling up the cable to the feedpoint
to raise the noise floor and cover weak signals.
Description:
The MFJ-918WM, MFJ-2919WM, and MFJ-2920WM are designed to provide balun
protection at building entrances, on a tower, or on the boom of a directional antenna. Sturdy
insulated five-way binding posts secure antenna pigtails or open-wire line. The balun's weather-
proof enclosure-cover is made from UV-resistant black ABS and is attached to a sturdy aluminum
panel with a universal mounting bracket assembly. On the inside, high-permeability ferrite beads
are installed over RG-303 Teflon coax to ensure high power handling, maximum suppression,
and minimal signal loss. Coax is connected to a premium quality Teflon-insulated SO-239 and a
panel-mounted stud is provided for a ground connection.
Models:
[ ] MFJ-918WM:
A 1:1 ratio 50-Ohm current balun designed to minimize losses and deliver
superior suppression over the entire HF range.
[ ] MFJ-2919WM:
A 4:1 ratio transmission-line transformer style balun designed for 200-Ohm
loads.
[ ] MFJ-2920WM:
A 9:1 ratio transmission-line transformer design for 450-Ohm applications.
Installation:
The enclosure may be wall mounted, tower mounted, or installed on an antenna
boom. Where possible, always install with the black-ABS enclosure facing up for maximum
weather protection. When wall-mounting on an insulated surface such as wood, provide a
ground-rod for protection. It won't prevent catastrophic damage from a direct strike, but can save
equipment from damage induced by nearby hits. Mounting holes are provided for mounting the
enclosure to a building or support plate. These holes may be enlarged or new ones installed to
accommodate U-bolts.
Coax
Ground
Antenna or
Balanced Line
Important Warning: To prevent accidental death or serious injury, never install an antenna
where it can contact power lines. Also, to prevent dangerous RF burns, keep energized
antenna surfaces out of reach to humans and animals.
